Despite the availability of low-cost, efficacious interventions to prevent mother-to-child HIV transmission (pMTCT), and significant investments to increase their availability, the translation of scientific advances into practice has been sub-optimal. In highly affected regions in sub-Saharan Africa (sSA), HIV-infected pregnant women navigate a complex, sequential cascade of pMTCT services. Due to this complex care cascade, pediatric HIV infection remains largely uncontrolled, including in Mozambique and Kenya. To simplify the cascade and improve pMTCT, the World Health Organization (WHO) released updated guidelines in 2013 to include Option B+, in which HIV-infected women initiate life-long anti-retroviral therapy (ART) during pregnancy regardless of CD4 count. Option B+ was adopted in Mozambique and Kenya in 2014, but initial results show sub-optimal ARV adherence and retention. Multiple health system challenges to Option B+ implementation exist; including the need to support the expanded role of nurses in service management and clinical care of Option B+ eligible mother-infant pairs. Decision-support tools tailored to nurses are needed to help their identification of systems inefficiencies and solutions across the HIV care cascade. As part of a cluster randomized trial of a systems analysis and improvement approach to assess and iteratively improve pMTCT in three sSA countries, we developed and evaluated an Excel(r)-based pMTCT cascade analysis tool (PCAT) that provides a systems-level view for nurses to rapidly and independently track patient flow through the pMTCT cascade. When combined with continuous quality improvement, the intervention was associated with a 4-5 fold greater rate of increase in coverage of maternal ARV provision and HIV-exposed infant screening. But the PCAT's usability was inhibited by low computer availability and literacy, and use was led by study nurses rather than facility personnel. Option B+-specific steps (e.g. retention in care and adherence), were also not part of the PCAT. Provider decision- support tools that are easily managed by health workers are more acceptable, usable and have more potential to improve management of complex health services. Tools tailored to specific environments with engagement from clinic staff are more likely to be implemented. In this study, we plan to adapt and refine a beta-tested version of a phone-based PCAT application, and test its usability and feasibility in Mozambique and Kenya. This study will collect preliminary data to inform a larger, controlled trial of the mobile PCAT application for Option B+ (mPCAT) and build capacity to conduct this trial in both countries. Aims include: 1) Identify Option B+-specific cascade measures and incorporate into the mPCAT; 2) Assess the usability of the mPCAT among nurses experienced with systems analysis and improvement for Option B+; 3) Feasibility test the mPCAT as part of a broader systems analysis and improvement approach.